Question

muriatic acid, found in hardware stores, is an impure solution of hci. it has several uses from cleaning swimming pools to treating concrete. what would be the ph of the hcl solution after addition of 45 ml of naoh

Answer 1

The pH of the HCl solution would be 4.158 after the addition of NaOH. Adding NaOH causes a smaller pH change in HCl compared to acetic acid.

Since HCl is a strong acid, we can assume that all of it dissociates. The initial concentration of H3O × is [H3O+] = 0.100 M. When the base solution is added, it also dissociates completely, providing OH ions. The H3O × and OH ions neutralize each other, so only those of the two that were in excess remain, and their concentration determines the pH. Thus, the solution is initially acidic (pH < 7), but eventually all the hydronium ions present from the original acid are neutralized, and the solution becomes neutral. As more base is added, the solution turns basic.

The total initial amount of the hydronium ions is:

pH = -log(6.95 × 10-5) = 4.158.

Comparing the titration curves for HCl and acetic acid, we see that adding the same amount of NaOH to both solutions causes a much smaller pH change for HCl than for acetic acid. This is consistent with the qualitative description of the shapes of the titration curves.